When an ion accelerates through a potential difference of 2160 v its electric potential energy decreases by 3.46×10−16 j . what is the charge on the ion?

We do as follows:

energy = charge x voltage change .

Let q be the charge then E = q V 

and solving for q we have
 
q = E / V = -1.37e-5J / 2850V = -4.81x10-9 C

Hope this answers the question. Have a nice day. 

Did you ever figue this

The magnets would be | n s | and | s n|